Going from 5 to 5s is supposed to be a minor upgrade and look what we got:
1) Better operating system
3) Bigger battery with 20% longer talk time
4) Better camera with more light sensitivity, better flash for low light photos, slow motion video, burst mode faster than lots of digital SLRs
5) Convenient one handed security with Touch ID
6) 64 bit SoC architecture designed in house by Apple under license from Arm Holdings for faster applications such as gaming.
7) Fastest screen response time in the industry
Just imagine what the 6 will be if that is a major upgrade.
You may be right. Apple has been too slow in coming out with new products since Steve Jobs died, so the sales may just be a very short-term reflection of many old iPhone users waited for too long to finally upgrade.